Burns, ulcerations, severe abrasions, skin transplants and similar poorly healing wounds affecting relatively large areas of skin are particularly vulnerable to infection. Artificial skins have been developed as bandages to temporarily protectively cover these wounds. These bandages must promote biofixation, control bacterial growth, supply moisture and prevent evaporation.
U.S. Pat. No. 3,849,238 (Gould et al.) discloses artificial skin comprising a water-containing hydrophilic polymer sponge layer and a thinner hydrophobic polymer layer. Illustrative of the hydrophilic polymers are hydroxyalkyl acrylates or methacrylates, acrylamides, and derivatives thereof. The hydrophobic component may be alkoxyalkyl acrylates or methacrylates, vinylacetate polymers, elastomeric silicone or polymerized olefins such as polyisoprene, polybutadiene or polyethylene.
U.S. Pat. No. 4,248,685 (Beede et al.) reports aqueous hydrocolloidal dispersions of random interpolymers having bacteriostatic properties. These interpolymers can initially be prepared as gels. Gelled material can then be cast into a self-supporting, transparent, conformable film wound dressing. The interpolymers are derived from the polymerization of a monomer mixture comprising 10-90% alpha, beta-olefinically unsaturated carboxylic acid esters with 90-10% alpha, beta-olefinically unsaturated amides capable of being dispersed in water. A difunctional monomer such as N,N.sup.1 -methylene bisacrylamide must also be present to cross-link the polymer mixture.
U.S. Pat. No. 4,554,317 (Behar et al.) describes a synthetic hydrophilic membrane for use as a wound covering. The membrane is prepared by graft polymerization of a hydrophilic monomer with a polyurethane substrate. Included among the hydrophilic monomers are acrylamides, hydroxyalkyl acrylates and hydroxyalkyl methacrylates. Gamma radiation and x-rays are suggested as suitable for initiating the graft polymerization.
Wound dressings described in the foregoing art are frequently opaque. Visual observation of the healing process is therethrough prevented. Infection or other complications cannot be detected with opaque coverings. Transparent wound dressings would therefore be highly desirable.
Transparent wound dressings are known. A particularly useful form is the gel type which can be cast as a sheet or strip. This type is commercially available, for instance, from Geistlich-Pharma Inc., Atlanta, Ga., under the trademark of GELIPERM. Sheets or strips have the advantage of easy usage, removability without disturbing healing, and promoting improved healing without excess granuloma formation. Most of the aforecited patents disclose compositions unsuitable for casting.
U.S. Pat. No. 4,556,056 (Fischer et al.) discloses transparent gels in sheet or strip form for use as fluid bandages. These sheets are produced by dissolving a monomer and a gellable polysaccharide in water and therein initiating free-radical polymerization of the monomer. While the compositions of this patent substantially improve over the cited art, problems do remain. In particular, the sheets of Fischer et al. as embodied in the GELIPERM product have clinically exhibited too rapid an uptake of moisture Moreover, the preferred polysaccharides described therein tend to gel too severely on wetting causing greater difficulty in handling the components as they are cast into sheets. Control of sheet quality and rate of production also thereby suffer.
Consequently, it is an object of this invention to provide a dressing which is sufficiently transparent to view a wound.
Another object of this invention is to provide a dressing of the sheet or strip variety.
A further object of this invention is the formulation of a dressing that is easily handlable for casting.
A final object of this invention is production of a sheet dressing exhibiting improved control over water absorption.